System for selectively receiving either 4-channel or- 2-channel stereophonic broadcastings

ABSTRACT

The invention relates to a system for selectively receiving either 4-channel 2-channel stereophonic broadcastings. The 4channel signal is a composite of stereophonic signals comprising a main channel signal, a pilot sub-carrier, a first sub-channel signal, a second sub-channel signal and a composite signal of 2channel stereophonic signals comprising a main channel signal, a pilot sub-carrier, and a first sub-channel signal. Transmission and reception are accomplished by inserting and superimposing, with respect to the composite signal of the 2-channel stereophonic signals, a modulated wave which is obtained by modulating a carrier wave of a frequency which is four times that of the pilot sub-carrier with a program signal differing from the 2-channel signals in a band corresponding to the second subchannel signal of the composite signal of the 4-channel stereophonic signals.

United States Patent [1 1 Mawake et a1.

1 1 Apr. 29, 1975 221 Filed: Jan. 17,1973

21 Appl.No.:324.561

[58] Field o1Search.... 179/15 ET, 1 GO. 100.4 ST, l79/100.l TD

[56] References Cited UNITED STATES PATENTS 3.679.832 7/1972 Halpern179/15 BT 3,708,623 H1973 Dorrcn 179/15 BT 3,787,629 l/l974 Limbcrg i179/15 BT OTH ER PUBLICATIONS Ouadrasonics on the Air by Feldman AudioMagazine Jan. 1970.

The Quart Broadcasting System by Gerzon Audio Magazine Sept. 1970.

Compatible FM Broadcasting of Panoramic Sound by Gibson et al. JournalABS Dec. 72.

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas D'Amico[57] ABSTRACT The invention relates to a system for selectivelyreceiving either 4-channel 2-channel stereophonic broadcastings. The4-channel signal is a composite of stereophonic signals comprising amain channel signal, a pilot sub-carrier, a first sub-channel signal. asecond sub-channel signal and a composite signal of 2- channelstereophonic signals comprising a main channel signal, a pilotsub-carrier. and a first sub-channel signal. Transmission and receptionare accomplished by inserting and superimposing, with respect to thecomposite signal of the Z-channel stereophonic signals, a modulated wavewhich is obtained by modulat ing a carrier wave of a frequency which isfour times that of the pilot sub-carrier with a program signal differingfrom the Z-channel signals in a band corresponding to the secondsub-channel signal of the composite signal of the 4-channel stereophonicsignals.

6 Claims, 6 Drawing Figures use MOD

l 30 MAIN r CARRIER osc 26 27 SWITCHING PULSE 118 FREQ 4 SEN cm GEN MODI 20 1 uglcea I 19 25 MAIN ost:

1 SYSTEM FOR SELECTIVELY RECEIVING EITHER 4-CI-IANNEL OR- Z-CI-IANNELSTEREOPHONIC BROADCASTINGS BACKGROUND OF THE INVENTION This inventionrelates generally to a transmitting and receiving system of stereophonicbroadcastings and more particularly to a system capable of receivingtwochannel stereophonic broadcasts and four-channel stereophonicbroadcastings by switching from one to the other.

Heretofore, various sytems have been proposed for stereophonicbroadcasting systems. In general, information signals obtained from alarge number of sound sources are transmitted as signals of a pluralityof channels. Each channel is reproduced on the receiving side by meansof a plurality of loudspeakers, to impart a stereophonic orthree-dimensional sound sensation to the listeners.

A system representative of these known systems is a 2-channelstereophonic broadcasting system which depends on a carrier-suppressionAM-FM system. In the operation, this system, simultaneously transmits: asum signal (L R) comprising left (L) and right (R) channel signals, apilot sub-carrier of a 19 KHz frequency which is slightly higher thanthe upper limit frequency of the sum signal band; and anamplitude-modulated wave of the difference signal (L R) of a two-channelsignal in a form resulting from the suppression of a carrier wave of afrequency of 38 KHz which is twice that of the pilot sub-carrier, and asignal wave generated by frequency modulating a carrier wave of a 67 KHzfrequency with a signal (which may be a program signal of a differentkind) other than the above mentioned stereophonic signal. These signalsoccupy respective divided frequency bands.

A frequency modulated wave of a signal other than the stereophonicsignal may be obtained. The frequency of the stereophonic carrier waveis 67 KHz and has no higher-harmonic relationship with respect to thefrequency of 38 KHz of the carrier wave of the amplitude-modulated wave.For this reason, a large number of standard oscillators are necessary ascarrier-wave sources on the transmission side. On the receiving side,there are difficulties such as the generation of much interference noisein the received signals.

A so-called Dorren system which is 4-channel stereophonic broadcastingsystem is compatible with the 2- channel stereophonic broadcastingsystem depending on a carrier suppression AM-FM system which hasrecently been practiced in an experimental broadcasting in the U.S.A.

SUMMARY OF THE INVENTION It is a general object of the invention toprovide a new and useful transmitting and receiving system capable ofreceiving either this 4-channel stereophonic broadcasting signal or aZChannel stereophonic broadcasting including program signals ofdifferent kinds.

Another object of the invention is to provide a transmitting andreceiving system of 2-channel 4-channel stereophonic broadcastingchangeover type wherein, in 2-channel stereophonic broadcasting, thefrequency of a carrier wave modulated by program signals of differentkinds for multiplexing by frequency division is made equal to thefrequency of a higher harmonic of a pilot subcarrier. In the systemaccording to the present invention, a large number of standardoscillators are not required as carrier wave sources on the transmittingside. Furthermore, on the receiving side, there is no large amount ofinterference noise.

Still another object of the invention is to provide a system capable ofpositively accomplishing the above stated Z-channel 4-channelstereophonic broadcasting changeover. In this case, the program signalsof different kinds are amplitude modulated for multiplexing on the2-channel stereophonic broadcasting.

A further object of the invention is to provide a system wherein it ispossible to separate automatically and receive a 4-channel stereophonicbroadcasting and a 2-channel stereophonic broadcasting wherein programsignals of different kinds are multiplexed without the necessity ofproviding any changeover means.

Further objects and features of the invention will be apparent from thefollowing detailed description when read in conjunction with theaccompanying drawings, throughout which like parts are designated bylike reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a block diagram showing one embodiment of transmittingapparatus of a system according to the invention;

FIGS. 2A and 2B are graphical representations respectively indicatingthe frequency spectrums of a 4- channel stereophonic broadcasting signaland of a 2- channel stereophonic broadcasting signal resulting from themultiplexing of different program signals;

FIG. 3 is a block diagram showing one embodiment of receiving apparatusfor receiving signals transmitted by the transmitting section shown inFIG. 1;

FIG. 4 is a block diagram showing another embodiment of transmittingapparatus of a system according to the invention; and

FIG. 5 is a block diagram showing one embodiment of receiving apparatusfor receiving signals transmitted by the transmitting apparatus shown inFIG. 4.

DETAILED DESCRIPTION One embodiment of transmitting apparatus of thesystem of the present invention is illustrated in FIG. 1. Left-front andleft-rear channel signals LF and LR are supplied to a 76 KHZ switchingcircuit 15 through input terminals 11 and 12, respectively. Right-frontand right-rear channel signals RF and RR are introduced to a KI-Izswitching circuit 16 through input terminals 13 and 14. The switchingcircuits l5 and 16 receive switching pulses from a switching pulsegenerating circuit 20. A signal of I52 KHz frequency from a mainoscillator I9 is formed into these switching pulses of 76 KHz, withsuccessively lagged switching phases.

Signals which have been successively switched and time divided by the 76KHz pulses are supplied from the switching circuits l5 and 16respectively to a 38 KHz switching circuit I7, where they arealternately switched by two switching pulses of mutually opposite phasesupplied by the switching pulse generating circuit 20. These switchingpulses are then sent out to a terminal 18.

The switching circuits l5, l6 and I7 constitute a switching multiplexcircuit (time-division multiplex circuit). The composite signal Cappearing at the output terminal 18 may be represented by the followingequation, when the signals applied to terminals 11 through 14 are the4-channel signals LF, LR, RF, and RR.

C A+B sin wt D cos out C sin 2mt The frequency spectrum of thiscomposite signal C (FIG. 2A) comprises a direct wave of the signal A asa main channel signal, amplitude-modulated waves of signals B and Dresulting from the suppression of the carrier wave of 38 KHz as a firstsub channel signal, and amplitude-modulated signals of the signal Cresulting from the suppression of the carrier wave of 76 KHz as a secondsub-channel signal.

When the signals applied to the input tenninals 11 through 14 areZ-channel signals LF LR L and RF RR R, the composite signal C' appearingat the output terminal 18 may be represented by the following equation.

CI"): (L R) sinmt The frequency spectrum of this composite signal C'(FIG. 28) comprises a direct wave of the signal (L R) as a main channelsignal and amplitudemodulated signals of the (L R) signal resulting fromthe suppression of the carrier wave of 38 KHz as a first sub-channelsignal.

As is apparent from a comparison of FIGS. 2A and 28, a 2-channel signalcomponent does not exist as a second sub-channel signal in the caseillustrated in FIG. 28. For 2-channel signal broadcasting, this vacantsecond sub-channel signal band has superimposed thereon a modulated waveproduced by modulating a 76 KHz carrier wave with program signals ofdifferent kinds.

A pilot signal generator 21 operates when supplied with a signal fromthe main oscillator 19, to generate a pilot sub-carrier of 19 KHz andsend this signal to an adder 22. The pilot sub-carrier of 19 KHz addedin the adder 22 to the signal from the terminal 18 corresponds to aposition indicated by the letters fp in FIGS. 2A and 2B.

A switch 23 is connected between the terminal 18 and the adder 22. Itsstationary contact point a is connected directly to the terminal 18. Thestationary contact point b is connected through an attenuator 24 to theterminal 18. This attenuator 24 prevents overmodulation when, duringmultiplexing of 2-channel stereophonic signals and program signals ofdifferent kinds. The level of the 2-channel stereophonic signalcomponent is lowered to frequency modulate the main carrier wave withthe composite signal.

If the signals applied to the input terminals 11 through 14 are4-channel signals LF, LR, RF, and RR, the movable contact of the switch23 is connected with the contact point a The output signal of theswitching circuit 17 is supplied directly to the adder 22. If thesignals applied to the input terminals 11 through 14 are 2-channelsignals L(=LF=LR) and R(=RF, RR), the selector contact of the switch 23is connected to the contact point 12,, whereby the output signal of theswitching circuit 17 is supplied by way of the attenuator 24 to theadder 22.

A carrier oscillator 25 generates a 76 KHz carrier wave when a signal issupplied thereto from the main oscillator 19. A frequency modulator 26(such as a serrasoid modulator, for example) modulates this carrier.Program signals of different kinds are applied as a modulation wavethrough a terminal 27 to the frequency modulator 26.

Between the frequency modulator 26 and the adder 22, there is connecteda switch 28 having a movable contact which is changed over inintercoupled relationship with the movable contact of the aforedescribedswitch 23. This switch 28 has an unused idle contact point 0 and acontact point b connected to the frequency modulator 25. The movablecontact of the switch 28 is switched to the contact point a when themovable contact of the switch 23 is changed over to the contact pointa,, and when the movable contact of the switch 23 is changed over to itscontact point b,, that of the switch 28 is switched to its contact pointb Accordingly, if the input signal is a Z-channel signal, the movablecontact of the switch 28 is switched to its contact point b Afrequency-modulated wave is obtained by frequency modulating the 76 KHZcarrier wave with program signals of different kinds, supplied to theadder 22. The frequency spectrum of this frequency-modulated wave is asindicated in the second sub-channel signal zone in FIG. 2B. It isapparent from a comparison of FIGS. 2A and 2B that the 76 KHz carrierwave component is large, in this case.

The output of the adder 22 is applied as a modulating wave to afrequency modulator 29, where a carrier wave from a main carrier waveoscillator 30 is frequency modulated. The resulting output signal ofthis frequency modulator is led out through an output terminal 31 andtransmitted from a transmitting antenna (not shown).

The signal thus transmitted is received by receiving apparatus oneembodiment of which described below with reference to FIG. 3. The radiosignal is received by a receiving antenna 40 and passed through acircuit 41 including a high frequency amplifier, a frequency converter,an intermediate frequency amplifier, and other parts, to a frequencydemodulator 42. A compos ite signal is produced on the output side ofthis frequency demodulator.

This composite signal is supplied to a narrow bandpass filter 43, wherethe frequency components in the vicinity of 76 KHz are filtered. Theresulting signal is supplied to a switch control circuit 44. If thereare different kinds of programs in the above mentioned composite signal,there is a large 76 KHz carrier wave component, as indicated in FIG. 2B.For this reason, an output of relatively high level is obtained from thefilter 43.

If the composite signal is a 4-channel stereophonic signal, the 76 KHzcarrier wave component is suppressed. The output signal of the filter 43is nonexistent, or its level is extremely low. The switch controlcircuit 44 operates in accordance with the output signal of the filter43 to form a control signal for switching. The movable contacts ofswitches 45 and 46 are activated by the output control signal of theswitch control circuit 44. For the switches 45 and 46, suitableswitching means such as relays and electronic switches can be used.

The switch 45 has an unused stationary contact point a and a stationarycontact point b connected to the output side of the frequencydemodulator 42. The switch 46 has a stationary contact point a,connected to the output side of the frequency demodulator 42 and acontact point b connected to the output side of a low-pass filter 47.This filter 47 has a filtering characteristic such that the main channelsignal and the first sub-channel signal of the composite signal are inpassing bands, while the second sub-channel signal is in a non-passingband.

Furthermore, the composite output signal of the frequency demodulator 42is supplied to a narrow bandpass filter 48, where a pilot signal of 19KHz is filtered. This pilot signal is supplied to a generator 49 forgenerating 38 KHz switching pulses and to a generator 50 for generating76 KHz switching pulses.

The movable contact of the switch 46 is connected to a switching circuit51, which carries out a switching operation in response to switchingpulses of 38 KHz from the switching-pulse generator 49. The output sideof this switching circuit 51 is connected to switching circuits 52 and53, which respectively are activated by 76 KHz switching pulses from theswitching pulse generator S0 to carry out switching.

When the composite signal obtained from the frequency demodulator 42 isa signal corresponding to a 4-channel stereophonic signal, the movablecontacts of the switches 45 and 46 are switched to their contact pointsa and a.,, respectively. When the composite signal obtained from thefrequency demodulator 42 is a multiplexed signal comprising differentkinds of program signals and a 2-channel stereophonic signal, themovable contacts of the switches 45 and 46 are respec' tively switchedto their contact points b and b.,.

If the received signal contains different kinds of program signals, themovable contact of the switch 45 is switched to its contact point b Thesignal passing through the switch 45 is supplied to a band-pass filter54. The signal of the second sub-channel band is in a state wherein ithas been frequency modulated by program signals of different kinds whichhave been filtered out in the filter 54 is supplied to a frequencydemodulator 55. The different kinds of program signals thus demodulatedby the frequency demodulator is led out through an output terminal 60.

When the apparatus is in the state wherein program signals of differentkinds are being obtained from the terminal 60, the high-level outputsignal produced by the switch control circuit 44 responsive to the 76KHz signal component derived by the narrow band-pass filter 43 causesthe movable contact of the switch 46 to make contact with the contactpoint [7,. The demodulated signals of the frequency demodulator 42 aresuch that only the main channel signal and the first subchannel signalcomponent pass through the low-pass filter 47. The switch 46 is suppliedto the switching circuit 51 for demodulation and further to theswitching circuits 52 and 53. As a result of the demodulation due to theswitching circuits 51, 52, and 53 for demodulation, a signal LF LF L isproduced as an output at terminals 56 and 57. A signal RF RR R isproduced as output at terminals 58 and 59.

When the receiving apparatus is in the state wherein it is receiving a4-channel stereophonic broadcasting,

a 76 KHz signal component is not derived from the narrow band-passfilter 43. The output signal of the switch control circuit 44 is of lowlevel. Consequently, the movable contacts of the switches 45 and 46 areswitched to their contact points 0 and 1 The signal supply to thecircuit for demodulation and reproduction of the different kinds ofprogram signals is interrupted. At the same time, the output signal ofthe frequency demodulator 42, is supplied without passing through thelow-pass filter 47, to the switching circuits 51, 52, and 53 fordemodulation. From the output terminals 56, S7, 58, and 59, are obtained4-channel signals LF, LR, RF, and RR.

By the practice of the present invention, as described above, selectiveswitching can be effected for receiving a 4-channel stereophonicbroadcasting system compatible with a 2-channel stereophonicbroadcasting system depending on a carrier-suppression AM-FM system.When the switching occurs, the system may receive from a broadcastingsystem 2-channel stereophonic program signals, different kinds of whichare so transmitted after being frequency divided and multiplexed at thetransmission band position of a second subchannel signal in the4-channel stereophonic broadcasting system. Accordingly, on thetransmission side, only a small number of standard oscillators isrequired. On the receiving side, the receiving circuit is automaticallyswitched in accordance with the broadcasting system to be received.Absolutely no noise is generated responsive to the presence of othersignals in the reproduced signal of the stereophonic signal and in thereproduced signal of different kinds of program signals. Anotheradvantageous feature of this system is that the frequency of the carrierwave modulated with different kinds of program signals is equal to thefrequency (a quadrupled frequency in the instant embodiment) of a higherharmonic of the frequency of the pilot subcarrier. For this reason,there is no possibility of interference noise mutually between signals.

As is known, if the level of the frequency component of the carrier wavebecomes low in a frequencymodulated wave, in a state other than that ofno modulation, the frequency component of the carrier wave positionbecomes zero in some cases. In the foregoing embodiment, a frequencycomponent in the vicinity of four times the frequency value of a pilotcarrier exists only if a frequency-modulated wave, due to differentkinds of program signals, is in the second sub-channel band of thecomposite signal. This frequency component is extracted and used tocarry out automatic switching of the above mentioned circuits. For thefrequency-modulated wave described above, the above mentioned automaticcircuit switching operation of the receiver is apt to become unreliable.

As one measure to solve this problem, an amplitude modulator is used inplace of the frequency modulator 26 in the transmitting apparatusillustrated in FIG. 1. An amplitude demodulator is used in place of thefrequency demodulator 55 in the receiving apparatus shown in FIG. 3. Inthis case, it becomes possible to switch selectively between a 4-channelstereophonic broadcasting system compatible with a Z-channelstereophonic broadcasting system depending on a carriersuppression AM-FMsystem and a broadcasting system wherein, with respect to a 2-channelstereophonic broadcasting system depending on a carriersuppression AM-FMsystem, different kinds of program signals are transmitted after beingfrequency divided and multiplexed in the form of an amplitude modulatedwave in the transmission band position of the second sub-channel signalin a 4-channel stereophonic broadcasting system.

On the receiver side, the switching of the receiving circuits isautomatically carried out in accordance with the presence or absence ofa carrier wave in the second sub-channel signal band. In thisconnection, it will be obvious that a 76 KHz carrier wave is used forthe amplitude modulation wave of the program of different kinds, andcarrier suppression is not carried out.

In the system of this embodiment, a carrier wave is always present inthe second sub-channel signal band. This gives rise to a problem. Unlessthe entire level of the composite signal is lowered, the frequencymodulation due to the composite signal with respect to the main carrierwave becomes overmodulation. In this case, there is a poorsignal-to-noise ratio at the time of Z-channel stereophonic broadcastingincluding program signals of different kinds. In addition, a circuit forautomatic switching is necessary in the receiver in each of the abovedescribed embodiments. Consequently, the circuit organization of thereceiver becomes complicated and expensive.

These difficulties can be overcome by a system as described below withrespect to one embodiment as illustrated in FIGS. 4 and 5.

FIG. 4 is a block diagram indicating the organization of thetransmitting apparatus of the system, in which parts which are the sameas or equivalent to those of the embodiment shown in FIG. 1 aredesignated by like reference numerals and characters, and detaileddescription thereof will not be repeated.

In this transmitter, a main oscillator 70 generates a l9 KHz frequencysignal. This signal is supplied as a pilot sub-carrier directly to theadder 22 and, at the same time, to a frequency multiplier 72 within aswitching pulse generating circuit 71. The frequency signal which hasthus been doubled in the frequency multiplier 72 is supplied to a 38 KHzswitching pulse generating circuit 74 and to a frequency multiplier 73.The frequency signal which has been further doubled by the frequencymultiplier 73 is supplied to a 76 KHZ switching pulse generating circuit75 and to a 90 phase shifter 76.

The switching pulse generating circuits 74 and 7S supply respectiveswitching pulse trains having specifi cally required repetition cyclicperiods and initial phases, respectively, to the switching circuits l5,l6, and I7. Thereupon, these circuits operate similarly as in theembodiment illustrated in FIG. I to switch the 4- channel signals LF,LR, RF, and RR applied through the input terminals 11 through 14 and tosend out timedivided, multiplexed signals.

The output phase-shift signal of the 90 phase shifter 76 is supplied asa carrier wave to a ring modulator '77 and there subjected to balancedamplitude modulation by a modulation signal of programs of differentkinds from the terminal 27. This carrier wave supplied to the ringmodulator 77 has a frequency which is 4 times that of the pilotsub-carrier. Moreover, the carrier has a phase difference of 90 relativeto the phase of the carrier wave of the second sub-channel signal usedat the time of 4channel stereophonic signal transmission.

Accordingly, if the 4-channel signals applied to the input terminals llthrough 14 are signals LF, LR, RF,

and RR, the movable contacts of the switches 23 and 28 are respectivelyin contact with their contact points a, and a and the composite signal Cobtained on the output side of the adder 22 with the transmitter in thisstate can be represented by the following equation.

4 (at C sin 20:! +asin If the 4-channel signals applied to the inputterminals 11 through 14 are LF=LR=L and RF=RR=R, the movable contacts ofthe switches 23 and 28 are respectively connected to the contact pointsb, and h The composite signal C' obtained on the output side of theadder 22, with the transmitter in this state, can be represented by thefollowing equation.

The signals occupying the second sub-channel signal band mutually have a90 phase difference.

A difference of 90 exists between the phases of carrier waves (switchingpulses) used in the demodulation of the second sub-channel signals inthe composite signals C and C' represented by the above two equations.For this reason, when the composite signal C is received by a receiverfor 4-channel stereophonic broadcastings different kinds of programsignals do not become mixed, as interference within the stereophonicsignals to generate noise, whereby only true and normal 2 channelstereophonic signals are reproduced.

Furthermore, when 4-channel stereophonic broadcasting is received in areceiving apparatus for different program signals, the apparatus is heldin a state wherein there is no demodulation output. Hence, two kinds ofbroadcast signals can be received merely by adding a receiving apparatusfor different program signals into a receiver for 4-channel stereophonicbroadcastings. In this case, it is not necessary to provide an automaticswitching device for preventing interference mixing.

One embodiment of receiving apparatus for receiving radio signalstransmitted by the transmitting apparatus shown in FIG. 4 is illustratedby block diagram in FIG. 5. In FIG. 5, parts which are the same as orequivalent to those of the embodiment shown in FIG. 3 are designated bylike reference numerals, and detailed descrip tion thereof will not berepeated.

The output signal of the frequency demodulator 42 is supplied to theswitching circuit 51 and, at the same time, to a narrow band-pass filterand a band-pass filter 85. A 19 KHZ pilot sub-carrier is thus filteredby the filter 80. After passing through an amplifier circuit 8], it isdoubled by a multiplier 82 and supplied to a multiplier 83 and to a 38KHz switching pulse generating circuit 84. The resulting signal has beenfurther doubled by the multiplier 83 to a frequency of 76 KHz and issupplied to a phase shifter 87 and to a switching pulse generatingcircuit 88. The output switching pulses of the switching pulsegenerating circuit 84 are supplied to the switching circuit 51. Theoutput switching pulses of the switching pulse generating circuit 88 aresupplied to the switching circuits S2 and 53.

A signal of the second sub-channel signal band part, which has beenfiltered by the band-pass filter 85, is

supplied to a 76 KHZ switching circuit 86. A signal passed through the90 phase shifier 87 is applied to this switching circuit 86.

In the receiver of the above described organization, a 4-channelstereophonic broadcast depending on the so-called Dorren system is beingreceived. The four channel signals are demodulated by the switchingoperations of the switching circuits 51, 52, and 53. Four channelsignals LF, LR, RF, and RR are individually led out of the terminals 56,57, 58, and 59. In this case, no output appears at the output terminal60.

If the receiver is receiving a Z-channel stereophonic broadcastingwherein difierent program signals are multiplexed, the demodulationaction due to the switching operations of the switching circuits 51, 52,and 53 causes a signal L to appear as an output at the output terminals56 and 57 and a signal R to appear as output at the output terminals 58and 59. in this case, different program signals are produced as outputat the output terminal 60 responsive to the demodulation action due tothe switching operation of the switching circuit 86.

The system of the instant embodiment affords automatic separation andreception of a 4-channel stereophonic broadcasting depending on theso-called Dorren system and a Z-channel stereophonic broadcastingwherein diffrent program signals are multiplexed. There is no need forany provision of any means whatsoever for changing over or switchingtherebetween. Furthermore, since the signal of the second subchannelsignal band is a carrier-suppression, amplitude modulation wave,transmission is possible with a better signal-to-noise ratio state ofthe broadcasting wave which is FM transmitted than the system of theabove described embodiment. Since those skilled in the art will perceivemodifications, the appended claims are to be construed to cover allequivalent structures falling within the scope and the spirit of theinvention.

What we claim is:

l. A system for transmitting either 4-channel signals or Z-channelsignals comprising:

main oscillator means for generating a pilot signal having apredetermined frequency;

first oscillator means responsive to the pilot signal for generating afirst signal having a frequency which is twice that of the pilot signal;

second oscillator means responsive to the first signal for generating asecond signal having a frequency which is four times that of the pilotsignal; composing means;

means responsive to the first and second signals and to first, second,third and fourth channel signals for operating said composing means toproduce a first composite signal including a first main channel signal,a first suppressed carrier subchannel signal and a second suppressedcarrier subchannel signal, said first main channel signal being a sumsignal of the first, second, third and fourth channel signals, saidfirst suppressed carrier subchannel signal having a first carrier of afrequency equal to twice the predetermined frequency and having a firstmodulating signal modulated on the first carrier and a second modulatingsignal modulated in quadrature with the first carrier, said firstmodulating signal being the first channel signal plus the second channelsignal minus the third channel signal minus the fourth channel signal,said second modulating signal being the first channel signal minus thesecond channel signal minus the third channel signal plus the fourthchannel signal, said second suppressed carrier subchannel signal havinga second carrier of a frequency equal to four times the predeterminedfrequency and having a third modulating signal modulated on the secondcarrier, said third modulating signal being the first channel signalminus the second channel signal plus the third channel signal minus thefourth channel signal;

means for also operating said composing means responsive to the firstand second signals and to fifth and sixth channel signals for producinga second composite signal including a second main channel signal and athird suppressed carrier subchannel signal, said second main channelsignal being a sum signal of the fifth and sixth channel signals, saidthird suppressed carrier subchannel signal having a third carrier of afrequency equal to twice the predetermined frequency and having a fourthmodulating signal modulated on the third carrier, said fourth modulatingsignal being a difference signal between the fifth and sixth channelsignals; modulating means for modulating the second signal with aprogram signal which is different from the fifth and sixth channelsignals and for producing a non-suppressed carrier subchannel signal;

first switching means for passing the non-suppressed carrier subchannelsignal from said modulating means responsive to the second compositesignal produced by said composing means and for interrupting thenon-suppressed carrier subchannel signal responsive to the firstcomposite signal produced by said composing means;

means for adding the output signal of said composing means, the pilotsignal and the output signal of said switching means to produce4-channel signals responsive to the first composite signal produced bysaid composing means and to produce the 2- channel signals responsive tothe second composite signal and the program signal produced by saidcomposing means; and

means for transmitting the output signal of said adding means.

2. A receiving system for selectively reproducing either 4-channelsignals or Z-channel signal, said 4- channel signals including a firstmain channel signal, a pilot signal having a predetermined frequency, afirst suppressed carrier subchannel signal and a second suppressedcarrier subchannel signal, said first main channel signal being a sumsignal of first, second, third and fourth channel signals, said firstsuppressed carrier subchannel signal having a first carrier of afrequency equal to twice the predetermined frequency and having a firstmodulating signal modulated on the first carrier and a second modulatingsignal modulated in quadrature with the first carrier, said firstmodulating signal being the first channel signal plus the second channelsignal minus the third channel signal minus the fourth channel signal,said second modulating signal being the first channel signal minus thesecond channel signal minus the third channel signal plus the fourthchannel signal, said second suppressed carrier subchannel sig nal havinga second carrier of a frequency equal to four times the predeterminedfrequency and having a third modulating signal modulated on the secondcarrier, said third modulating signal being the first channel signalminus the second channel signal plus the third channel signal minus thefourth channel signal; said 2- channel signals including a second mainchannel signal, the pilot signal, a third suppressed carrier subchannelsignal and a non-suppressed carrier subchannel signal, said second mainchannel signal being a sum signal of fifth and sixth channel signals,said third suppressed carrier subchannel signal having a third carrierof a frequency equal to twice the predetermined frequency and having afourth modulating signal modulated on the third carrier, said fourthmodulating signal being a difference signal between the fifth and sixthchannel signals, said non-suppressed carrier subchannel signal having afourth carrier which frequency is equal to four times the predeterminedfrequency and having a program signal modulated on the fourth carrier;said receiving system comprising:

first filter means responsive to the 4-channel signals and the 2-channelsignals for passing the pilot signal; first generator means responsiveto the output signal of said first filter means for generating a signalhaving a frequency which is twice the frequency of the pilot signal;second generator means responsive to the output signal of said firstfilter means for generating a signal having a frequency which is fourtimes the frequency of the pilot signal; second filter means responsiveto the 2-channel signals for passing the carrier of the non-suppressedcarrier subchannel signal; control signal generating means responsive tothe output signal of said second filter means for producing a controlsignal during the time while the carrier of the non'suppressed carriersubchannel signal is present; third filter means responsive to the4-channel signals and the 2-channel signals for passing the first mainchannel signal and the first suppressed carrier sub channel signal amongthe 4-channel signals, and the second main channel signal and the thirdsuppressed carrier subchannel signal among the 2- channel signalsrespectively; demodulator means responsive to the 2-channel signals forreproducing the program signal; first switching means responsive to thecontrol signal for passing the Z-channel signals to said demodulatormeans responsive to the control signal and for interrupting the passageof any 4-channel signals to said demodulator responsive to an absence ofthe control signal; second switching means responsive to the controlsignal for passing the output signal of said third filter meansresponsive to the control signal and for bypassing said third filtermeans responsive to an absence of the control signal; and separatingmeans responsive to the output signal of said second switching means andthe output signals of the first and second generator means forseparating the first, second, third and fourth channel signals duringthe time while the 4-channel signals are present, and for separating thefifth and sixth channel signals during the time while the Z-channelsignals are present. 3. A system for transmitting either 4-channelsignals or Z-channel signals comprising:

main oscillator means for generating a pilot signal having apredetermined frequency;

first oscillator means responsive to the pilot signal for generating afirst signal having a frequency which is twice that of the pilot signal;

second oscillator means responsive to the first signal for generating asecond signal having a frequency which is four times that of the pilotsignal;

composing means responsive to the first and second signals and to first,second, third and fourth channel signals for producing a first compositesignal including a first main channel signal, a first suppressed carriersubchannel signal and a second suppressed carrier subchannel signal,said first main channel signal being a sum signal of the first, second,third and fourth channel signals, said first suppressed carriersubchannel signal having a first carrier of a frequency equal to twicethe predetermined frequency and having a first modulating sig nalmodulated on the first carrier and a second modulating signal modulatedin quadrature with the first carrier, said first modulating signal beingthe first channel signal plus the second channel signal minus the thirdchannel signal minus the fourth channel signal, said second modulatingsignal being the first channel signal minus the second channel signalminus the third channel signal plus the fourth channel signal, saidsecond suppressed carrier subchannel signal having a second carrier of afrequency equal to four times the predetermined frequency and having athird modulating signal modulated on the second carrier, said thirdmodulating signal being the first channel signal minus the sec ondchannel signal plus the third channel signal minus the fourth channelsignal;

means for also operating said composing means responsive to the firstand second signals and to fifth and sixth channel signals to produce asecond composite signal including a second main channel signal and athird suppressed carrier subchannel signal, said second main channelsignal being a sum signal of the fifth and sixth channel signal, saidthird suppressed carrier subchannel signal having a third carrier of afrequency equal to twice the predetermined frequency and having a fourthmodulating signal modulated on the third carrier, said fourth modulatingsignal being a difference signal between the fifth and sixth channelsignals;

phase-shifting means responsive to the second signal for phase-shiftingthe second signal by modulating means for modulating the output signalof said phase-shifting means with a program signal which is differentfrom the fifth and sixth channel signals to produce a modulated signal;

switching means for passing the modulated signal from said modulatingmeans responsive to the second composite signal produced by saidcomposing means and for interrupting the modulating means responsive tothe first composite signal produced by said composing means;

means for adding the output signal of said composing means, the pilotsignal, and the output signal of said switching means so that 4-channelsignals are produced responsive to the first composite signal producedby said composing means and 2-channel signals including the programsignal are produced responsive to the second composite signal producedby said composing means; and

means for transmitting the output signal of said add ing means.

4. A receiving system for selectively reproducing either 4-channelsignals or 2-channel signals, said 4- channel signals including a firstmain channel signal, a pilot signal having a predetermined frequency, afirst suppressed carrier subchannel signal and a second suppressedcarrier subchannel signal, said first main channel signal being a sumsignal of first, second, third and fourth channel signals, said firstsuppressed carrier subchannel signal having a first carrier of afrequency equal to twice the predetermined frequency and having a firstmodulating signal modulated on the first carrier and a second modulatingsignal modulated in quadrature with the first carrier, said firstmodulating signal being the first channel signal plus the second channelsignal minus the third channel signal minus the fourth channel signal,said second modulating signal being the first channel signal minus thesecond channel signal minus the third channel signal plus the fourthchannel signal, said second suppressed carrier subchannel signal havinga second carrier of a frequency equal to four times the predeterminedfrequency and having a third modulating signal modulated on the secondcarrier, said third modulating signal being the first channel signalminus the second channel signal plus the third channel signal minus thefourth channel signal; said 2- channel signals including a second mainchannel signal, the pilot signal, a third suppressed carrier subchannelsignal and a fourth subchannel signal, said second main channel signalbeing a sum signal of fifth and sixth channel signals, said thirdsuppressed carrier subchannel signal having a third carrier of afrequency equal to twice the predetermined frequency and having a fourthmodulating signal modulated on the third carrier, said fourth modulatingsignal being a difference signal between the fifth and sixth channelsignals, said fourth subchannel signal having a fourth carrier of afrequency equal to four times the predetermined frequency and whichphase is in quadrature with that of the second carrier, and having aprogram signal modulated on the fourth carrier; said receiving systemcomprising:

first filter means responsive to the 4-channel signals and the 2-channelsignals for passing the pilot signal;

first generator means responsive to the output signal of said firstfilter means for generating a signal having a frequency which is twicethe frequency of the pilot signal;

second generator means responsive to the output signal of said firstgenerator means for generating a signal having a frequency which istwice the frequency of the output signal of said first generator means;

second filter means for passing the second suppressed carrier subchannelamong the 4-channel signals and for passing the fourth subchannel amongthe 2-channel signals;

phase-shifting means responsive to the output signal of said secondgenerator means for phase-shifting the output signal of said secondgenerator means by demodulator means responsive to the output signal ofsaid phase-shifting means and the output signal of said second filtermeans for reproducing the program signal; and

separating means responsive to the 4-channel signals and the outputsignals of said first and second generator means for separating thefirst, second, third and fourth channel signals responsive to the 4-channel signals, and responsive to the 2-channel signals and the outputsignals of said first and second generator means for separating thefifth and sixth channel signals responsive to the Z-channel signals.

5. A transmitting system as defined in claim 1 further comprisingattenuator means for attenuating the level of the output signal of saidcomposing means; and second switching means cooperative with said firstswitching means for passing the output signal of said attenuator meansduring the time when said composing means produces the second compositesignal and for bypassing the attenuator means during the time when saidcomposing means produces the first composite signal; said adding meansadding the output signal of said second switching means, the secondsignal, and the output signal of said switching means.

6. A transmitting system as defined in claim 3 further comprisingattenuator means for attenuating the level of the output signal of saidcomposing means; and second switching means cooperating with saidswitching means for passing the output signal of said attenuator meansduring the time while said composing means produces the second compositesignal and for bypassing the attenuator means during the time while saidcomposing means produces the first composite signal; said adding meansadding the output signal of said second switching means, the secondsignal and the output signal of said switching means.

1. A system for transmitting either 4-channel signals or 2channelsignals comprising: main oscillator means for generating a pilot signalhaving a predetermined frequency; first oscillator means responsive tothe pilot signal for generating a first signal having a frequency whichis twice that of the pilot signal; second oscillator means responsive tothe first signal for generating a second signal having a frequency whichis four times that of the pilot signal; composing means; meansresponsive to the first and second signals and to first, second, thirdand fourth channel signals for operating said composing means to producea first composite signal including a first main channel signal, a firstsuppressed carrier subchannel signal and a second suppressed carriersubchannel signal, said first main channel signal being a sum signal ofthe first, second, third and fourth channel signals, said firstsuppressed carrier subchannel signal having a first carrier of afrequency equal to twice the predetermined frequency and having a firstmodulating signal modulated on the first carrier and a second modulatingsignal modulated in quadrature with the first carrier, said firstmodulating signal being the first channel signal plus the second channelsignal minus the third channel signal minus the fourth channel signal,said second modulating signal being the first channel signal minus thesecond channel signal minus the third channel signal plus the fourthchannel signal, said second suppressed carrier subchannel signal havinga second carrier of a frequency equal to four times the predeterminedfrequency and having a third modulating signal modulated on the secondcarrier, said third modulating signal being the first channel signalminus the second channel signal plus the third channel signal minus thefourth channel signal; means for also operating said composing meansresponsive to the first and second signals and to fifth and sixthchannel signals for producing a second composite signal including asecond main channel signal and a third suppressed carrier subchannelsignal, said second main channel signal being a sum signal of the fifthand sixth channel signals, said third suppressed carrier subchannelsignal having a third carrier of a frequency equal to twice thepredetermined frequency and having a fourth modulating signal modulatedon the third carrier, said fourth modulating signal being a differencesignal between the fifth and sixth channel signals; modulating means formodulating the second signal with a program signal which is differentfrom the fifth and sixth channel signals and for producing anon-suppressed carrier subchannel signal; first switching means forpassing the non-suppressed carrier subchannel signal from saidmodulating means responsive to the second composite signal produced bysaid composing means and for interrupting the non-suppressed carriersubchannel signal responsive to the first composite signal produced bysaid composing means; means for adding the output signal of saidcomposing means, the pilot signal and the output signal of saidswitching means to produce 4-channel signals responsive to the firstcomposite signal produced by said composing means and to produce the2channel signals responsive to the second composite signal and theprogram signal produced by said composing means; and means fortransmitting the output signal of said adding means.
 2. A receivingsystem for selectively reproducing either 4-channel signals or 2-channelsignal, said 4-channel signals including a first main channel signal, apilot signal having a predetermined frequency, a first suppressedcarrier subchannel signal and a second suppressed carrier subchannelsignal, said first main channel signal being a sum signal of first,second, third and fourth channel signals, said first suppressed carriersubchannel signal having a first carrier of a frequency equal to twicethe predetermined frequency and having a first modulating signalmodulated on the first carrier and a second modulating signal modulatedin quadrature with the first carrier, said first modulating signal beingthe first channel signal plus the second chAnnel signal minus the thirdchannel signal minus the fourth channel signal, said second modulatingsignal being the first channel signal minus the second channel signalminus the third channel signal plus the fourth channel signal, saidsecond suppressed carrier subchannel signal having a second carrier of afrequency equal to four times the predetermined frequency and having athird modulating signal modulated on the second carrier, said thirdmodulating signal being the first channel signal minus the secondchannel signal plus the third channel signal minus the fourth channelsignal; said 2-channel signals including a second main channel signal,the pilot signal, a third suppressed carrier subchannel signal and anon-suppressed carrier subchannel signal, said second main channelsignal being a sum signal of fifth and sixth channel signals, said thirdsuppressed carrier subchannel signal having a third carrier of afrequency equal to twice the predetermined frequency and having a fourthmodulating signal modulated on the third carrier, said fourth modulatingsignal being a difference signal between the fifth and sixth channelsignals, said non-suppressed carrier subchannel signal having a fourthcarrier which frequency is equal to four times the predeterminedfrequency and having a program signal modulated on the fourth carrier;said receiving system comprising: first filter means responsive to the4-channel signals and the 2-channel signals for passing the pilotsignal; first generator means responsive to the output signal of saidfirst filter means for generating a signal having a frequency which istwice the frequency of the pilot signal; second generator meansresponsive to the output signal of said first filter means forgenerating a signal having a frequency which is four times the frequencyof the pilot signal; second filter means responsive to the 2-channelsignals for passing the carrier of the non-suppressed carrier subchannelsignal; control signal generating means responsive to the output signalof said second filter means for producing a control signal during thetime while the carrier of the non-suppressed carrier subchannel signalis present; third filter means responsive to the 4-channel signals andthe 2-channel signals for passing the first main channel signal and thefirst suppressed carrier subchannel signal among the 4-channel signals,and the second main channel signal and the third suppressed carriersubchannel signal among the 2-channel signals respectively; demodulatormeans responsive to the 2-channel signals for reproducing the programsignal; first switching means responsive to the control signal forpassing the 2-channel signals to said demodulator means responsive tothe control signal and for interrupting the passage of any 4-channelsignals to said demodulator responsive to an absence of the controlsignal; second switching means responsive to the control signal forpassing the output signal of said third filter means responsive to thecontrol signal and for bypassing said third filter means responsive toan absence of the control signal; and separating means responsive to theoutput signal of said second switching means and the output signals ofthe first and second generator means for separating the first, second,third and fourth channel signals during the time while the 4-channelsignals are present, and for separating the fifth and sixth channelsignals during the time while the 2-channel signals are present.
 3. Asystem for transmitting either 4-channel signals or 2-channel signalscomprising: main oscillator means for generating a pilot signal having apredetermined frequency; first oscillator means responsive to the pilotsignal for generating a first signal having a frequency which is twicethat of the pilot signal; second oscillator means responsive to thefirst signal for generatinG a second signal having a frequency which isfour times that of the pilot signal; composing means responsive to thefirst and second signals and to first, second, third and fourth channelsignals for producing a first composite signal including a first mainchannel signal, a first suppressed carrier subchannel signal and asecond suppressed carrier subchannel signal, said first main channelsignal being a sum signal of the first, second, third and fourth channelsignals, said first suppressed carrier subchannel signal having a firstcarrier of a frequency equal to twice the predetermined frequency andhaving a first modulating signal modulated on the first carrier and asecond modulating signal modulated in quadrature with the first carrier,said first modulating signal being the first channel signal plus thesecond channel signal minus the third channel signal minus the fourthchannel signal, said second modulating signal being the first channelsignal minus the second channel signal minus the third channel signalplus the fourth channel signal, said second suppressed carriersubchannel signal having a second carrier of a frequency equal to fourtimes the predetermined frequency and having a third modulating signalmodulated on the second carrier, said third modulating signal being thefirst channel signal minus the second channel signal plus the thirdchannel signal minus the fourth channel signal; means for also operatingsaid composing means responsive to the first and second signals and tofifth and sixth channel signals to produce a second composite signalincluding a second main channel signal and a third suppressed carriersubchannel signal, said second main channel signal being a sum signal ofthe fifth and sixth channel signal, said third suppressed carriersubchannel signal having a third carrier of a frequency equal to twicethe predetermined frequency and having a fourth modulating signalmodulated on the third carrier, said fourth modulating signal being adifference signal between the fifth and sixth channel signals;phase-shifting means responsive to the second signal for phase-shiftingthe second signal by 90*; modulating means for modulating the outputsignal of said phase-shifting means with a program signal which isdifferent from the fifth and sixth channel signals to produce amodulated signal; switching means for passing the modulated signal fromsaid modulating means responsive to the second composite signal producedby said composing means and for interrupting the modulating meansresponsive to the first composite signal produced by said composingmeans; means for adding the output signal of said composing means, thepilot signal, and the output signal of said switching means so that4-channel signals are produced responsive to the first composite signalproduced by said composing means and 2-channel signals including theprogram signal are produced responsive to the second composite signalproduced by said composing means; and means for transmitting the outputsignal of said adding means.
 4. A receiving system for selectivelyreproducing either 4-channel signals or 2-channel signals, said4-channel signals including a first main channel signal, a pilot signalhaving a predetermined frequency, a first suppressed carrier subchannelsignal and a second suppressed carrier subchannel signal, said firstmain channel signal being a sum signal of first, second, third andfourth channel signals, said first suppressed carrier subchannel signalhaving a first carrier of a frequency equal to twice the predeterminedfrequency and having a first modulating signal modulated on the firstcarrier and a second modulating signal modulated in quadrature with thefirst carrier, said first modulating signal being the first channelsignal plus the second channel signal minus the third channel signalminus the fourth channel signal, said second modulating signal being thefirst channel signal minus The second channel signal minus the thirdchannel signal plus the fourth channel signal, said second suppressedcarrier subchannel signal having a second carrier of a frequency equalto four times the predetermined frequency and having a third modulatingsignal modulated on the second carrier, said third modulating signalbeing the first channel signal minus the second channel signal plus thethird channel signal minus the fourth channel signal; said 2-channelsignals including a second main channel signal, the pilot signal, athird suppressed carrier subchannel signal and a fourth subchannelsignal, said second main channel signal being a sum signal of fifth andsixth channel signals, said third suppressed carrier subchannel signalhaving a third carrier of a frequency equal to twice the predeterminedfrequency and having a fourth modulating signal modulated on the thirdcarrier, said fourth modulating signal being a difference signal betweenthe fifth and sixth channel signals, said fourth subchannel signalhaving a fourth carrier of a frequency equal to four times thepredetermined frequency and which phase is in quadrature with that ofthe second carrier, and having a program signal modulated on the fourthcarrier; said receiving system comprising: first filter means responsiveto the 4-channel signals and the 2-channel signals for passing the pilotsignal; first generator means responsive to the output signal of saidfirst filter means for generating a signal having a frequency which istwice the frequency of the pilot signal; second generator meansresponsive to the output signal of said first generator means forgenerating a signal having a frequency which is twice the frequency ofthe output signal of said first generator means; second filter means forpassing the second suppressed carrier subchannel among the 4-channelsignals and for passing the fourth subchannel among the 2-channelsignals; phase-shifting means responsive to the output signal of saidsecond generator means for phase-shifting the output signal of saidsecond generator means by 90*; demodulator means responsive to theoutput signal of said phase-shifting means and the output signal of saidsecond filter means for reproducing the program signal; and separatingmeans responsive to the 4-channel signals and the output signals of saidfirst and second generator means for separating the first, second, thirdand fourth channel signals responsive to the 4-channel signals, andresponsive to the 2-channel signals and the output signals of said firstand second generator means for separating the fifth and sixth channelsignals responsive to the 2-channel signals.
 5. A transmitting system asdefined in claim 1 further comprising attenuator means for attenuatingthe level of the output signal of said composing means; and secondswitching means cooperative with said first switching means for passingthe output signal of said attenuator means during the time when saidcomposing means produces the second composite signal and for bypassingthe attenuator means during the time when said composing means producesthe first composite signal; said adding means adding the output signalof said second switching means, the second signal, and the output signalof said switching means.
 6. A transmitting system as defined in claim 3further comprising attenuator means for attenuating the level of theoutput signal of said composing means; and second switching meanscooperating with said switching means for passing the output signal ofsaid attenuator means during the time while said composing meansproduces the second composite signal and for bypassing the attenuatormeans during the time while said composing means produces the firstcomposite signal; said adding means adding the output signal of saidsecond switching means, the second signal and the output signal of saidswitching means.